Patients with severe symptoms of chronic venous disease (i.e. with one or more following features: severe pain, swelling, (commonly clinically measured from grade 1 thru 3 representing pitting edema, (1) ankle edema (2) and gross swelling involving the limb (3), measured using a type of plethysmography) stasis dermatitis, venous ulcer) generally go through a battery of tests to determine the cause of disease, where testing includes duplex scans, venous function tests, ambulatory pressure measurements, arm/foot pressure tests, air plethysmography, contrast venography, CT venography and magnetic resonance venography. Clinical evaluation alone can be used to diagnose and grade severity of CVD, for instance, using the classes pursuant to clinical CEAP classification, such as C3-C6 scores for diagnosing more severe forms of CVD in the affected limb (C 0-2 an also be an indicator if severe symptoms of pain are present), but clinical evaluation alone cannot diagnose the pathology of the disease. Causes of CVD are generally attributable to obstruction (also called stenosis) or reflux or a combination. If a thrombotic or non-thrombotic vein lesion(s) causing venous obstruction or stenosis is diagnosed using the existing testing protocols (such as pressure measurements, duplex scans, venography and CT/MR imaging), then intravascular imaging techniques intravascular ultrasound (IVUS) can be used to determine the exact obstruction location and extent; percutaneous balloon angioplasty and/or stent placement is used to treat the obstruction at the same time. IVUS typically provides more detail of the obstructive lesion than venography and often the true extent of the lesion per IVUS is more severe than suggested by venography.
IVUS is a medical imaging methodology using a specially designed catheter with a miniaturized ultrasound probe attached to the distal end of it. The proximal end of the catheter is attached to computerized ultrasound equipment. Several companies manufacture and market this device. IVUS allows the application of ultrasound technology to image the vein wall including obstructive lesions. The physician positions the tip of a guidewire, such as a 0.32 inch guidewire (Glidewire, Terumo, Somerset, N.J.) with a very soft and pliable tip and about 200 cm long. The physician steers the guidewire from outside the body, though angiography catheters and into the blood vessel branch to be imaged. The ultrasound catheter tip (such as a 6F transducer) is slid in over the guidewire and positioned, within the vein of interest. The sound waves are emitted from the catheter tip, are usually in the 10-20 MHz range, and the catheter also receives and conducts the return echo information out to the external computerized ultrasound equipment which constructs and displays a real time ultrasound image of a thin section of the blood vessel currently surrounding the catheter tip, usually displayed at 30 frames/second image. A desired length of the vein can be imaged by slowly withdrawing the IVUS catheter over the guidewire.
The (a) blood vessel wall inner lining, (b) fibrosis within the wall and (c) connective tissues covering the outer surface of the blood vessel are echogenic, i.e. they return echoes making them visible on the ultrasound display. By contrast, the blood containing lumen itself is relatively echolucent, just black circular spaces, in the images.
The primary disadvantages of IVUS are its' expense, there is an increase in the time needed to perform the procedure, and the fact that it is an invasive interventional procedure. In the venous system, IVUS imaging techniques are generally not employed unless a diagnosis of obstruction is made using standard testing protocols (such as duplex, venography etc.). If obstruction is indicated, a single puncture provides the access for IVUS interrogation device (for instance, in the thigh area). A guidewire is used to insert the imaging catheter into the interior of the veins, and after the anatomy is defined with IVUS, the same guidewire is used for percutaneous stent placement. The procedure is usually performed in the operating room or angiography suite with the patient under general anesthesia though local anesthesia and intravenous sedation are acceptable in many patients.